1. The Field of the Invention
The present invention relates to communication systems and in particular to a communication terminal interface via a terminal interface device to a communication network that presents power to the terminal interface device that may be tapped for operational power.
2. Present State of the Art
Modern data transmission devices such as computers are increasingly used in applications that require exchange of data over a communication network. Popular networks for use in propagating data include well established telephone networks. Such networks were originally designed to accommodate, and therefore propagate, the transmission of voice conversations which include very specific bands of frequencies. Individual countries have implemented unique power and frequency standards relating to their particular implementation of telephone networks.
While the interoperation specifications differ for national telephone networks, they each require the modulation of computer data in order to comply with the individual specific bandwidth requirements. To facilitate the modulation and the complementary demodulation processes, devices known as modems (MOdulate/DEModulate) have become ubiquitous. In order to compatibly interoperate with the telephone network, a modem must perform certain xe2x80x9ctelephone handsetxe2x80x9d functions to appear to the telephone network as a legacy telephone handset-compatible device.
One such telephone handset function that the modem must perform is the function of being able to go xe2x80x9coff-hook.xe2x80x9d Off-hook functionality requires the modem to signal the telephone network that information is either going to be sent by the modem to the telephone network or that the modem is ready to receive information from the telephone network. Telephone network specifications typically require that the modem or other terminal device signal an off-hook condition by drawing or sinking a specified amount of current from the telephone network. Traditionally, such drawn current was utilized by a telephone to xe2x80x9cpowerxe2x80x9d the telephone during use. In a modem application where a data device such as a computer requires appreciable power, the current drawn by the modem to simulate the off-hook condition was typically unnecessary for the modem and therefore wasted as the modem functionality derived power either from an external independent power supply or by sharing the power supply of the computer or host device.
In the advent of miniaturization, computers have become increasingly more integrated and as such have become more mobile and portable. One overriding design concern with portable computers is power management. In a portable environment, all of the operating power for the computer and any peripheral devices, such as modems, must be resident within the computer. Hence, portable computer batteries are heavily taxed by the data terminal (e.g., computer) functionality. Therefore, any inefficient use of available power affects the overall performance of the communication system (e.g., the data terminal (computer) and the network interface device (modem)).
As briefly alluded to above, modern networks may utilize existing communication networks such as POTS or other international similar networks. POTS provides an archaic interface that requires a specific amount of off hook current to be drawn. Power drawn had heretofore been unusable by devices since older devices required an amount of power for operation beyond what was available. With miniaturization and lower power designs, the available power from, for example, the POTS is sufficient to be employed for useful functionality to power electronic components on a network interface device (e.g., modem).
An additional requirement placed upon a telephone network interface device such as a modem is that the device cannot introduce virtually any noise onto the telephone system. therefore, the use of a transformer for coupling power from the terminal device over to circuitry on the network interface device that interfaces with the telephone network has become unruly and ineffective as frequencies have increased. Alternative coupling techniques and power management architectures are therefore in order.
Thus, what is needed is an apparatus for efficiently utilizing available power in a communication system to more efficiently manage scarce on-board power from a portable device such as a portable computer by utilizing available line power from the communication network during interaction therewith.
What is also needed is a power management architecture that minimizes the amount of noise generated from the circuitry on a network interface device that is injected back onto the communication network.
It is therefore an object of the present invention to provide an efficient power management circuit for incorporating into a terminal or network interface device, (e.g., a modem), that integrates minimal standby power from a data terminal device, (e.g., a computer), with available line current from a communication network, (e.g., a telephone network), in order to adequately power the network interface device with minimal power impact to the data terminal device.
It is yet a further object of the invention to minimize power transforming inefficiencies including the generation of noise associated therewith for an improved system for interfacing with a communication network and complying with the standards as required by communication networks.
It is therefore a further object of the present invention to provide a power circuit for incorporating into a network interface device, such as a modem, that is programmable for compatible operation in various international environments that employ varying communication network specifications including differing line or hold current levels to signal an off-hook condition
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a power circuit apparatus for improving upon power management including the compatible noise parameters associated therewith in network terminal devices, such as modems, that are deployed in portable environments wherein power management is critical is presented. The inventive apparatus includes a power circuit that exacts a fractional amount of data terminal device (e.g., computer) power to maintain minimal standby functionality within the network interface device and employs the otherwise wasted off-hook line current required to signal the, for example, modem""s active state to the communication network (e.g., POTS or similar standard).
The power circuit of the present invention, in its preferred embodiment, is comprised of a charge pump powered from standby power received from the data terminal device. The output from the charge pump within the power circuit preferably located within the network interface device is post regulated by a shunt regulator which creates a regulated output voltage for powering the standby circuitry. When the standby circuitry either detects a xe2x80x9cringxe2x80x9d signal as dispatched from the communication network or when the data terminal device signals the network interface device (e.g., modem) to open a channel with the communications network for originating a session, the network interface device goes xe2x80x9coff-hook.xe2x80x9d The network interface device initiates an off-hook condition by switching on a voltage regulator located across the communication network terminals. As recalled from is above, the off-hook condition is signaled to the communication network by drawing or sinking a requisite amount of line current, commonly called hold current or line current, from the communication network.
The augmented power supplied by the voltage regulator is converted from the voltage across the communication network terminals (e.g., tip and ring in the POTS environment). Any excess current from the voltage regulator is absorbed by the shunt regulator. Such a novel approach as described herein enables the two individual sources of power (i e., the standby power from the data terminal equipment as converted by the charge pump and the line power from the communication network as regulated by the voltage regulator) to be complementary without introducing contention issues at the regulated output voltage common node.
By using the hold current from the line or communication network side to power the voltage regulator and to supply the majority of the operational power, the inefficiencies associated with a charge pump-only design are minimized. Also, by using power from the line side (e.g., hold current) to power the terminal interface device circuitry during operation, the noise associated with alternative approaches such as transformer coupling of power from the terminal device side is greatly reduced and virtually eliminated.
The present invention also accommodates the multinational nature and use of modern network interface devices by incorporating a programmable hold current sub-circuit that may be programmably altered to conform with varying national standards relating to the requisite hold current that must be drawn from the communication network to signal an off-hook condition.
These and other objects and features of the present invention will be more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth herein.